In an automobile it is common to provide visible alarms as red lamps for warning the driver of defective conditions of the car as when the temperature of the radiator is high or if the engine is empty of oil. In an automobile circuit, it is also common to provide a buzzer or an alarm to warn the driver when he opens the door with the ignition in the "on" position, or in some instances even if the key remains in the ignition lock, or when the parking lights, or the main headlights, or radio, or other accessory devices in the automobile is energized when the vehicle is left unattended.
In other environments, particularly in automotive vehicles, alarm systems have been utilized to warn the driver that the vehicle is being left in an unsafe condition. For example, U.S. Pat. No. 3,723,968 discloses an alarm circuit for an automobile which sounds an alarm if both the parking brake is off and the driver's seat belt is not on.
Although these prior devices are useful, they do not warn the driver of several important and dangerous situations. For example, the visible alarm is not always effective because the driver must look at the road and sometimes encounter the danger before he becomes aware of the bad condition of the car. This system of alarm is not developed to warn of the danger as when the driver is driving and the parking brake is on, or the radiator does not contain enough water, or the tire does not contain enough air, or the belt of the engine is snapped, or the generator of the car does not create electricity. Therefore, it is necessary to have the kind of alarm which timely warns the driver about any defective conditions of the vehicle. Some of these alarms relate to a circuit which will warn the driver that one or more accessory devices are energized when the ignition has been switched to the "off" position.